Work and energy - Class 9

 1:- What is work?

Ans:- Work is said to be done when we applied a force upon an object and the object displace from their mean position in any direction.   

It is a scaler quantity. It is denoted by 'W'.

Work done by a force on a body depends on two factors

👉 magnitude of force

👉Displacement through which the body moves 

W ∝ F

W ∝ s

So, W ∝ Fs

And, W = k Fs

The value of k in SI. unit is '1'. 

So, W = Fs

Work = Force × displacement

The SI. unit of force = Newton (N)

The SI. unit of displacement = metre (m)

Therefore SI. unit of work = Nm

It is also denoted by Joule (J)

     1Nm = 1 J

2:- What is 1 Joule work?

Ans:- 1 Joule work is the amount of work done on an object when a force of 1N displace it by 1m along the line of action of the force. 

 1 Joule = 1 N × 1m

Notes:- Mental labour is not considered work as per science.

3:- What is the formula of work done If work and displacement are in same direction?

Ans:- If work and displacement are in same direction then work done is positive.

In this condition, the formula of work done is

W = Fs

3:- What is the formula of work done If work and displacement are in opposite direction?

 Ans:- If work and displacement are in opposite direction then work done is negative.

In this condition, the formula of work done is

W = - Fs

4:- When is the work done become '0'?

Ans:- If displacement is perpendicular to the force than work done is '0'.

 

Energy

1:- What is energy?

Ans:- The capacity of the body to do work is called energy of body.

 SI. unit of energy is Joule and it is denoted by 'J'.

              1KJ =  1000J 

2:- How many forms of energy?

Ans:- There are various forms of energy.

(1) Potential energy

(2) Kinetic energy

(3) Heat energy

(4) Chemical energy

(5) Electrical energy

(6) Light energy

3:- What is potential energy?

Ans:- Energy possessed by a body due to its position or shape is called potential energy.

       Ex:-

4:- What is kinetic energy? Write formula for kinetic energy.

Ans:- Energy possessed by a body due to its motion is called kinetic energy. Kinetic energy of an object increases with increasing its speed.  

Let an object of mass 'm', moves with uniform velocity 'u', the object displace 's', due to constant force 'F'.   Than work done = Force × displacement

                                   = F×s  ........... (1)

Due to force the velocity changes to 'v' and acceleration produced is 'a'.

So, relation between 'v', 'u', 's' and 'a' is. 

V² - u² = 2as

s =  V² - u²/2a ........... (2)

and F = ma ..............(3)     

    

chemical effects of electric current- Class 8

  What is electricity or electric current?

The flow of electric charge is known as Electric Current, Electric current is carried by moving electrons through a conductor.
By convention, electric current flows in the opposite direction to the movement of electrons.

Electric current is actually the movement of electrons.

Electric current is denoted by the letter ‘I’

S.I. unit of electric current is ampere (A).

                                      

2:- What is the formula of electric current?

Ans:- Electric current is expressed by the rate of flow of electric charges. Rate of flow means, the amount of charge flowing through a particular area in unit time.

If a net electric charge (Q) flows through a cross-section of a conductor in time t, then,

Where 

I = electric current, 

Q = net charge

t = time

3:- Write some metals that are conductor of electricity.

Ans:- gold, silver, brass, iron

4:- What is electric circuit?

Ans:- Electric circuit is a continuous and closed path of electric current.

5:-  What is LED?

Ans:- LED stands for Light Emitting Diode. It glows even when a weak current flows through it. LED has two leads attached to it. one lead is longer than other. The longer lead is always connected to the positive terminal of the battery and the shorter lead to the negative terminal of the battery.

                                            

6:- How can we use magnetic compass as a tester?

Ans:- Magnetic compass is a better tester because the deflection of the magnetic needle can be seen even if the current is small. We can use a magnetic compass as a tester by keeping it near the wire of circuit. When the current flows through the circuit then the magnetic needle of  magnetic compass shows deflection.

7:- Why does the tap water conductor of electricity?

Ans:- Tap water is conductor of electricity because tap water is not pure. It contains dissolved impurities like salt and natural minerals which make it conductor of electricity

8:- Why does the distilled water Non-conductor of electricity?

Ans:- distilled water is Non-conductor of electricity because distilled water is pure and free from salts and natural minerals.

9:- How can we make distilled water conductor?

Ans:- We can make distilled water conductor by adding salt and natural minerals. Presence of salt in a liquid make it a good conductor of electricity. Liquid that conduct electricity are solutions of acids, bases or salts.

10:- Write short notes on William Nicholson's invention.

Ans:- In 1800, William Nicholson, a British chemist, showed that bubbles of oxygen and hydrogen were produced if electrodes were immersed in water. He also showed that oxygen bubbles were formed at anode and hydrogen bubbles we3re formed at cathode. 

11:-  What are electrolytes?

Ans:- Substances that do not conduct electricity when solid, but do when molten or dissolved in water are called electrolytes.

Ex:- acids, metal oxides, metal hydroxides, and salt

12:- What is Electrolysis?

Ans:- Electrolysis is a method of separating bonded elements and compounds by passing an electric current through them. It uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. 

13:- What is electrolytic cell?

Ans:- An cell that uses electrical energy to drive a non-spontaneous redox reaction. In this cell electrical energy is converted to chemical energy is called electrolytic cell.

14:- Write a short notes on mechanism of electrolysis. 

Coal and petroleum / class 8 / Chapter-5 / New St. Mery English School

  Coal and petroleum class-8

1:- What are exhaustible natural resources?

Ans:- Those natural resources which are present in limited quantity in nature and are not likely to be exhausted by human activities are called exhaustible resources.

  Ex:Coal,petroleum,natural gas,minerals,forests etc.

2:- What are inexhaustible nature resources?

Ans:- Those natural resources which are present in unlimited quantity in nature and are not likely to be exhausted by human activities are called inexhaustible resources. 

Ex:- Sunlight, air, Water, etc.

3:-  What are renewable resources?

Ans:- The resources which cannot be exhausted even after continuous utilization and as once used up, can be replenished within a reasonable period of time is called renewable resources.

Ex:- Sun, wind, etc.

4:-  What are Non-renewable resources?

Ans:- The resources which can be exhausted after continuous utilization and as once used up, can not be replenished within a reasonable period of time is called Non-renewable resources.

Ex:- coal, petroleum, forest etc.

5:- What is fuel?Give example.

Ans:- Any combustible substance that is used to produce heat at a reasonable cost is called fuel.

Ex:- Cowdung, wood, paper, kerosene, charchol etc.

6:- What are fossil fuels? Write example.

Ans:- The fuels that are formed in nature from dead remains of plants and animals are called fossil fuels.

Ex:- coal, petroleum and natural gas.

7:- What is the use of  fossil fuels?

Ans:-  fossil Fuels burn to produce a large amount of heat and light. The heat can be used to cook food, run engines or to generate electricity.

8:- What is coal?

 Ans:-
Coal is a hard, black, combustible minerals that consist mainly of carbon. It is a sedimentary rock formed from the remains of plants.

                                                         

9:- What is carbonisation ?

Ans:- The slow process by which the dead plants buried deep under the earth have become coal is called Carbonisation. 

10:- What is carboniferous age?

Ans:-  The time period take to complete carbonisation is called carboniferous age. 

11:- What is the composition of coal?

Ans:- coal is a complex mixture of carbon, hydrogen and oxygen with some amount of nitrogen, sulphur and phosphorus.

12:- How many types of coal?

Ans:- There are three types of coal:

1:- Anthracite

2:- Bituminous 

3:- Lignite  

13:- What is anthracite?

Ans:- Anthracite is the best variety of coal. It has more than 90% of carbon content.

                                                            

14:- What is bituminous?

Ans:- Bituminous coal has about 65-70% of carbon content. It is better than lignite but worst than anthracite.

                                                               

15:- What is lignite?

Ans:- Lignite coal is brown coal. It has only 38-40% of carbon content. It is worst than anthracite and bituminous.

                                                                      

16:- Write five places of india where coal is found.

Ans:- west bengal, jharkhand, orissa, madhya pradesh and tamil nadu.

17:- What is destructive distillation of coal?

Ans:- The process of heating coal in the absence of air at 1000⁰c  is called the destructive distillation of coal. In destructive distillation of coal many useful organic and inorganic products are obtained like coke, coaltar and colgas.

18:- What is coke?

Ans:- The solid residue left after destructive distillation of coal is called coke. It contains about 98% carbon . It is almost pure form of carbon. It is porus and black it is used in the manufacture of steel and to extract many metals from there ores.

                                                                

19:- What happens when steam is passed over red hot coke?

Ans:- When steam is passed over red hot coke, it produces water gas.

              Carbon + water vapour → Water gas 

               C          +         H₂O        →  CO +    H₂

20:- What happens when air is passed over red hot coke?

Ans:- When air  is passed over red hot coke, it produces producer gas.

                  
            Carbon +          air         →   producer  gas 

                2C      +  O₂ +   4N₂  →   2 CO +    4N₂

21:- What is coal tar?

Ans:- Coal tar is a carbonic material that is a mixture of about 200 carbon compounds. It is a black, thick liquid with unpleasant smell.

                                                              

22:- Write some products that can we obtain from coal tar.

Ans:- Some products that can we obtain from coal tar are

👉 Coal tar is used in the manufacture of various substances like synthetic dyes, drugs, explosives, pesticides, perfume, plastic paints etc.

👉 Coal tar is used in the manufacture of pitch.

👉 Naphthalene balls are also obtained from coal tar.

23:- What is coal gas?

Ans:- The gas obtained during the processing of coal to get coke is called coal gas. It is a mixture of hydrogen , carbon monoxide and mithane.

                                                        

24:- What is the use of coal gas?

Ans:- Coal  gas is used as a fuel in many industries situated near the coal processing plant.

25:- What is petroleum?

Ans:- Petroleum is naturally occurring dark- coloured viscous liquid formed trapped under the ground. It is the complex mixture of various hydrocarbons mixed with water, salts and other particles. It is insoluble in water and lighter than water.

26:-  Why is petroleum called petroleum?

Ans:- petroleum is called petroleum  because it is found under the crust of earth trapped in rocks.

27:- How is petroleum formed?

Ans:- Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

28:- How can we obtain  crude oil and natural gas under the surface of earth ?

Ans:- We  can obtain  petroleum and natural gas by drilling holes in the earth's crust. When a well is drilled, natural gas first comes out with great pressure and after some times oil comes out.

29:- When and where the world's  first oil well was drilled?

Ans:- The world's  first oil well was drilled in pensylvania, USA, in 1859.

30:-  When and where the india's  first oil well was drilled?

Ans:- The india's  first oil well was drilled in makum, in assam , in 1867.

31:- What is refining?

Ans:- The process of separating various constituents of  petroleum by fractional distillation is called refining. It is carried out in a petroleum refinery.

                                                                
                                                                  

32:- Explain the process of refining of petroleum.

Ans:- In refining of petroleum, crude oil is heated to about 400 degree Celsius in a furnace and the vapours thus formed are passed into a tall fractionating tower.The hydrocarbons with highest bioling pionts condense first and are collected at the base of the fractionating tower. With the rising vapours, the hydrocarbons with the lower boiling points condense at different heights. 

👉 Petroleum gas has lower boilining point that is more than 25 degree celsius so consedense first and escape from the top of the tower.

👉Bitumen has higher boiling point that is more than 350 degree celsius so condense last and escape from the bottom of the tower.

33:-What is natural gas?

Ans:- Natural gas is a mixture of gases which are rich in hydrocarbons. All these gases like methane, nitrogen, carbon dioxide etc are naturally found in atmosphere. It is found along with petroleum under the earth.

34:- Write some uses of natural gas.

Ans:-   

1-compressed form of Natural gas is used as fuel for vehicles which is known as CNG.

 2- It is used as fuel for boilers and air conditioners worldwide.

3- Natural gas is used in the manufacture of many chemicals and fertilisers.

4- on strong heating, natural gas decomposes into carbon and hydrogen. this hydrogen is used in the production of ammonia.

35:- Write some places where natural gas found in India.

Ans:- Tripura, Rajasthan, Maharashtra, and in the krishna-Godawari delta

36:- Write four problems that arises due to overuse of fossil-fuels.

Ans:- Four problems that arises due to overuse of fossil-fuels are

1- Exhaustion of existing fossil fuels.

2- increasing in pollution of air, water, and soil

3- global warming

4- Energy crisis in future

37:-What do you mean by judicious use of energy?

Ans:- judicious use of energy means that we should not waste energy. We should use the energy with utmost care.

38:- How can we use energy judiciously? Write six ways.

Ans:- The six ways to use energy judiciously are

1- switch off lights, fans, etc, when not in use.

2-use applications like coolers, heaters, geysers, etc. only when needed.

3-reduce the flame while cooking food.

4- Use CFLs and tube lights, that use less less energy ,instead of bulbs

5- Use public transport in place of private vehicles.

6- Use pressure cookers and keep the vessels covered while cooking.

39:- How can we conserve Fossil fuels? Write five ways.

Ans:- The five ways by which we can conserve Fossil fuels are

1- Natural gas should be used as an alternative source of energy

2-Use of solar energy should be encouraged like solar cookers, solar heaters etc

3- Wind power should be used to generate electricity

4- Hydroelectric power should be generated from water-bodies with the help of dam.

5- Energy generated from biomass should be used in rural and semi-urban areas.  

Combustion and Flame - class 8

 1:- What is combustion?

Ans:- Combustion is a process of burning of a substance in the presence of air or oxygen along with the evolution of heat and light.

Ex:- When charcoal burns in air, it gives carbon dioxide, heat and light

         charcoal   + air   → carbon dioxide + heat + light 

             C         + O₂    →     CO₂             + heat + light    

 2:- What is combustible? write some example.

Ans:- The substance that undergoes combustion is called combustible. 

Ex:- wood, paper, kerosene, charcoal etc.

3:- What is non-combustible substance?

Ans:- A substance that doesnot undergo combustion is said to be non-combustible substance.

Ex:- bricks, stone, metal, soil  etc.

4:- What is fuel? give example.

Ans:- Any combustible substance that is used to produce heat at a reasonable cost is called fuel.

Ex:-  cow dung, wood, paper, kerosene, charcoal etc

5:- how many types of fuel? Name them.

Ans:- there are three types of fuel.

1- solid fuel ( Ex:- wood, paper, charcoal, cow dung etc. )

2- liquid fuel (Ex:- kerosene, petrol, LPG etc. )

3- gas fuel ( Ex:- biogas etc. )

6:- What is complete combustion?

Ans:-  A combustion is said to be a complete combustion when a fuel burns in sufficient amount of air.

Ex:- When methane completely burns in air produces carbon dioxide, heat and water

            Methane + oxygen → carbon dioxide + water + heat

               CH₄     +  O₂        →   CO₂              +   2H₂O + heat

7:- What is incomplete combustion?

Ans:- A combustion is said to be a incomplete combustion when a fuel burns in insufficient amount of air.

Ex:- When methane burns in insufficient amount of air produces carbon monoxide, water and very lesser amount of heat

            Methane + oxygen → carbon monoxide + water + heat

            2CH₄     +  3O₂      →     2CO                  + 4H₂O + heat

 

8:- Write three conditions that is necessary for combustion.

Ans:- The three conditions that is necessary for combustion are

1- Presence of a combustible substance.

2- Presence of a supporter of combustion

3-Attainment of ignition temperature of the combustible substance.

 

9:- What is the supporter of combustion? give example.

Ans:- Those substances that help the combustible substance in burning is known as supporter of combustion. 

EX:- oxygen or air

10:- why is a person covered with wool blanket when he catches fire?

Ans:- Combustion takes place in the presence of oxygen or air. A person covered with wool blanket when he catches fire because wool blanket cuts the supply of air and the fire gets extinguished.

11:- What is ignition temperature?

Ans:-  The lowest temperature at which a substance catches fire or starts burning is called its ignition temperature. Ignition temperature is also called kindling temperature.

12:- Why do paper or match stick not catch fire on their own?

Ans:- paper or match stick do not catch fire on their own because their temperature is less then their ignition temperature.

13:- What are inflammable substances? write example.

Ans:- The substances which have very low ignition temperature and can catch fire easily with a flame are called are called inflammable substances.

Ex:- petrol, alcohol, LPG etc.

14:- How does water help to put out the fire?

Ans:- Water brings down the temperature of the combustible material below its ignition temperature. This prevent the fire from spreading. In this process water vapour is also produced which surround the combustible material and cuts off the supply of air. Hence fire gets extinguished.

15:- Which types of fire can water not extinguish? Explain.

Ans:- Water can not extinguish the fire caused by electric short circuit because water may conduct electricity and give shock to the person trying to extinguish the fire.

Water can not extinguish the fire caused by oil and petrol because oil and petrol are lighter than water, it keeps burning on surface of water.

16:-How does Carbon dioxide help to put out the fire? 

Ans:- Carbon dioxide is heavier than oxygen. It forms a blanket around the fire and cutting the supply of air. Hence the fire is controlled.

 

17:-  Which types of fire can Carbon dioxide extinguish? Explain.

Ans:-Carbon dioxide can extinguish the fire caused by electrical short circuit, oil, kerosene, petrol etc.

18:- What is fire extinguisher?

Ans:- A fire extinguisher is a device used to extinguish small fires due to short circuits, petrol, oil etc.

 

19:- How does a fire extinguisher work?

Ans:- In a fire extinguisher cylinder, carbon dioxide gas is filled and stored under high pressure in liquid form. When carbon dioxide released from the cylinder, carbon dioxide expands enormously in volume and forms a blanket around the fire. It also decreases the temperature of the fuel below its ignition temperature. Hence the fire is controlled.  

20:- What is Rapid combustion? Give example

Ans:- The combustion reaction in which a large amount of heat and light are produced in a short time is called rapid combustion. It needs external heat to occur.

Ex:- burning of cooking gas, burning of kerosene

21:- What is spontaneous combustion? Give example.

Ans:- The combustion reaction which occur on its own without the help of any external heat is called Spontaneous combustion. Spontaneous combustion takes place at room temperature.

Ex:- burning of white phosphorus at room temperature, forest fires due to heat of sun.

22:- What is explosion? give example.

Ans:- A very fast combustion reaction in which a large amount of heat, light and sound are produced is called explosion.

Ex:- burning of crackers etc.

23:- Which types of combustible material produces flame?

Ans:- Those combustible material which vaporise on burning produces flames.

Ex:- candle produces flame due to vaporization of wax

Earthen lamp produces flame due to vaporization of ghee.

24:- Why does candle produce flame during burning?

Ans:- Candle produces flame during burning because candle has wicks, molten wax rises through the wicks and get vapourise. 

25:- Why does charcoal not produce flame during burning? 

Ans:- charcoal does not produce a flame during burning because It does not vapourise on burning.

26:- explain the structure of flame.

Ans:- The flame is generally spindle in shape. A flame has three main zones.

1- The outer non-luminous zone

2- The middle luminous zone

3- The innermost dark zone  

 1- The outer non-luminous zone- This is the hottest part of the flame. it is the complete combustion zone due to sufficient supply of air.The flame of this zone is blue in colour.       

 2- The middle luminous zone- this part of the flame is moderately hot and it is a zone of incomplete combution since the supply of air is not sufficient . A black residue is left on the object placed in this part of the flame. The colour of the flame is yellow in this zone.

3- The innermost dark zone- This is the least hot part of the flame ,near the wick of the candle. No combution takes place here due to lack of air. This zone contains unburnt wax vapours and so appears black in colour.                                                                                                                              

27:- when can we consider that a fuel is good? explain.

Ans:- A fuel is considered good if:-

👉 It burns easily in air.

👉 It produces a large amount of heat.

👉 It does not leave unwanted residues.

👉 It is easy to store and transport.

👉It is cheap and easily available.

28:- what is fuel efficiency ?

Ans:- The amount of energy released per unit mass of the fuel is called fuel efficient.

29 :- what is calorific value?

Ans:- The amount of heat energy produced by the combution of one kg of a fuel is called its calorific value. It is expressed in the unit of kilojoule per kg (kj/kg).

30:- which fuel has highest calorific value?

Ans:- Hydrogen.

31:- Why does hydrogen not use as domestic fuel?

Ans:- Hydrogen is not used as domestic fuel because its calorific value is very high. Therefore, it is not easy to handle.

32:- which fuel is used as spacecraft fuel?

Ans:- Liquid hydrogen.

33:- Write five harmful empects of burning fuels?

Ans:- The five empect of burning fuels are:-

1- Burning of fuels like wood,coal, petrolium produces unburnt carbon particles . These particles are very fine and can cause respiratory diseases, like asthma.

2- Combution of fuels add carbon dioxide to the atmosphere. Which leads to greenhouse effect and increase global warming.

3- Incomplete combution produces carbon monoxide piosonous gas and can cause death.

4- Burning of coal and diesel produce sulphur dioxide gas. This gas is highly poisonous and corrosive in nature. It dissolves in rain water to form acid. It destroys, crops, buildings, soil, etc.

5-Fumes from engines of vehicles contain oxides of nitrogen. These oxides also dissolve in rainwater to produce acid rain.